The term "asphalt" or "asphalt cement" as used in the description of the present application refers to any of a variety of solid or semi-solid materials at room temperature which gradually liquify when heated, and in which the predominant constituents are naturally occurring bitumens or which are obtained as residue in petroleum refining. Asphalt is further defined by Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 3, Third Ed. (1978) pp. 284-327, John Wiley & Sons, N.Y. An additional discussion appears in the publication entitled "A Brief Introduction to Asphalt and Some of its Uses", Manual Series No. 5 (MS-5), The Asphalt Institute, 7th Ed., September, 1974. Both of these references are hereby incorporated by reference.
Asphalt cements have found particular utility when combined with aggregates. Such combinations, generally referred to as "asphalt concrete", are employed extensively as paving compositions for roads, driveways, parking lots, airport runways, etc. The asphalt is converted to a fluid state when paving a road. One fluid form is the suspension or emulsion of the asphalt in water. After spreading and compressing the aggregate-containing asphalt, water evaporates or separates, and the asphalt hardens into a continuous mass. Another form of asphalt employed in road construction is a cutback, i.e., a liquid petroleum product produced by fluxing an asphaltic base with a suitable organic solvent or distillate. A road is formed by paving the aggregate-containing cutback and evaporating the volatile distillate from the mass. An advantage of using the above road construction techniques is the avoidance of high temperature application. In an alternative and most widely used technique, the asphalt and aggregate can be mixed and applied at elevated temperatures at the fluid state of the asphalt to form the road. This form of asphalt, which is neither cut-back nor emulsififed generally is referred to as asphalt cement.
The degree and rate of hardening of asphalt cement during application and while in service ("age hardening") are factors affecting the durability of a surface such as a road pavement. A certain amount of hardening of a freshly applied surface is often desirable in order to allow the newly placed surface to placed into service quickly. However, excessive hardening and loss of ductility of an asphalt based surface can dramatically reduce its useful lifetime. Januszke, in "Industrial Engineering Chemistry Product Research and Development", Vol. 10, (1971), 209-213, indicates that lead and zinc diethyldithiocarbamates were effective in inhibiting the adverse hardening.
In certain geographic areas, such as desert regions in the western and southwestern United States, deterioration of an asphalt road may occur quickly and is often extensive. Embrittlement and cracking of the road surface often result.
Because of the high demand for better quality materials for roofs and for the pavement of roads, airfields and other applications, there have been many suggestions in the art for producing improved asphaltic compositions.
It is known in the art that excessive age hardening of paving asphalts can be reduced through the use of certain antioxidants such as lead or zinc dithiocarbamates. The above-mentioned reference by Januszke discusses an evaluation of the effect of 24 antioxidants on paving asphalt durability and is incorporated by reference for its teachings regarding the problem and methods of assessing the performance of additives.
It also has been suggested, for example, that the properties of asphalt can be improved by incorporating into the asphalt, small amounts of maleic anhydride. In U.S. Pat. No. 2,347,626, a process is described for hardening asphaltic residues by reacting maleic anhydride with asphaltic petroleum residue containing unsaturated ingredients by heating the mixture to a temperature of from about 150.degree.-250.degree. C. until the softening point of the reaction product is substantially higher than that of the starting residue.
U.S. Pat. No. 4,139,511 describes asphalt compositions containing an epoxy resin, maleinated asphaltic materials obtained by reacting an asphaltic material with maleic anhydride and a ratio by weight of 100:0.2 to 100 at at a temperature of 100.degree.-300.degree. C. The asphaltic compositions also may contain a curing agent for the epoxy resin. U.S. Pat. No. 4,139,511 also describes in Cols. 1 and 2 , a number of Japanese publications including laid-open patent applications and publications in various Japanese Patent Gazettes which disclose asphaltic materials modified with various compositions such as (a) an adduct of maleic anhydride to asphalt with a polyhydric alcohol to produce a polyester containing hydroxyl groups which are then reacted with fatty acids for esterification; (b) bitumens containing carboxylic and/or acid anhydride groups and polymers or copolymers containing said groups (Japanese Patent Application Laying-Open Gazette No. 157415/75); bitumens modified with maleic anhydride and containing rubber-like materials such as styrene-butadiene rubber; bitumens containing epoxy resins and primary polyamines; etc.
U.S. Pat. No. 2,550,476 describes mineral aggregate bonding compositions which comprise a bitumen and a small amount of a condensation product prepared by reacting an olefin containing from 5 to 25 carbon atoms with an unsaturated dicarboxylic acid anhydride to form an intermediate which is then further reacted with a diamine. Only aliphatic olefins containing from 5 to 20 carbon atoms are described.